Republican Mark Sanford is seeking a political comeback nearly four years after admitting an affair. / Alex Wong, Getty Images

by Catalina Camia, USA TODAY

by Catalina Camia, USA TODAY

Former South Carolina governor Mark Sanford is addressing the extramarital affair that wrecked his marriage and damaged his political career, as he makes a direct appeal to voters in a new campaign ad.

"I've experienced how none of us go through life without mistakes, but in their wake we can learn a lot about grace, a God of second chances and be the better for it," Sanford says in the first TV commercial of his comeback bid for Congress.

"In that light, I humbly step forward and ask for your help in changing Washington," the Republican says.

Sanford was a rising political star mentioned as a potential presidential candidate when he tearfully admitted in 2009 to an affair with an Argentinean woman. He got a divorce in 2010 and quietly served out his term as governor.

Now, his old seat in the U.S. House is up for grabs and Sanford is one of 16 Republicans seeking to succeed Tim Scott, who was appointed to the U.S. Senate. Sanford is also engaged to Maria Belen Chapur, his former mistress.

Sanford is making his campaign about federal spending and the need to cut the size of government. He opens the ad with a knock on "Washington's math," which he says "doesn't add up." It's a message that helped get him elected to Congress three times before winning the race for governor.

Democrat Elizabeth Colbert Busch was endorsed over the weekend by South Carolina Rep. James Clyburn, his party's No. 3 leader in Washington. She is running against Ben Frasier.